FDS6670AS 查看數據表（PDF） - Richtek Technology

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FDS6670AS

6A, 24V, 600kHz Step-Down Converter with Synchronous Gate Driver

Richtek Technology 

RT8298

Function Block Diagram

VIN

VCC

EN/SYNC

VCC

Internal

Regulator

Enable

Comparator

1.7V +

-

5k

3V

OSC

Foldback

Control

Slope

Current Sense

Compensator Amplifier

+

-

OTP

VCC

UV Comparator

VCC

0.4V +

Switch

Controller

-

Current

6nA

VSS

15pF

0.808V

+

+EA

-

COMP

Signal

+

- Current

Comparator

BG

Driver

54pF 300k

FB

PGOOD

1pF

Comparator

0.75V +

-

RSENSE

45m

BOOT

SW

BG

PGOOD

Operation

The RT8298 is a synchronous high voltage Buck Converter

that can support the input voltage range from 4.5V to 24V

and the output current can be up to 6A. The RT8298 uses

a constant frequency, current mode architecture. In normal

operation, the high side N-MOSFET is turned on when

the Switch Controller is set by the oscillator (OSC) and is

turned off when the current comparator resets the Switch

Controller. While the N-MOSFET is turned off, the external

low side N-MOSFET is turned on by BG Driver with 5V

driving voltage from Internal Regulator (VCC) until next

cycle begins.

High side MOSFET peak current is measured by internal

RSENSE. The Current Signal is where Slope Compensator

works together with sensing voltage of RSENSE. The error

amplifier EA adjusts COMP voltage by comparing the

feedback signal (VFB) from the output voltage with the

internal 0.808V reference. When the load current

increases, it causes a drop in the feedback voltage relative

to the reference, the COMP voltage then rises to allow

higher inductor current to match the load current.

UV Comparator : If the feedback voltage (VFB) is lower

than threshold voltage 0.4V, the UV Comparator's output

will go high and the Switch Controller will turn off the high

Copyright ©2011 Richtek Technology Corporation. All rights reserved.

www.richtek.com

4

GND

side MOSFET. The output under voltage protection is

designed to operate in Hiccup mode.

Oscillator (OSC) : The internal oscillator runs at nominal

frequency 600kHz and can be synchronized by an external

clock in the range between 300kHz and 1.5MHz from EN/

SYNC pin.

PGOOD Comparator : This function is available for

RT8298ZQW only. When the feedback voltage (VFB) is

higher than threshold voltage 0.75V, the PGOOD open

drain output will be high impedance.

Enable Comparator : Internal 5kΩ resistor and Zener diode

are used to clamp the input signal to 3V. A 1.7V reference

voltage is for EN logic-high threshold voltage. The EN pin

can be connected to VIN through a 100kΩ resistor for

automatic startup.

Foldback Control : When VFB is lower than 0.7V, the

oscillation frequency will be proportional to the feedback

voltage.

Soft-Start (SS) : An internal current source (6nA) charges

an internal capacitor (15pF) to build the soft-start ramp

voltage (VSS). The VFB voltage will track the internal ramp

voltage during soft-start interval. The typical soft-start time

is 2ms.

is a registered trademark of Richtek Technology Corporation.

DS8298-01 November 2011

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